Full spine and full leg radiographic examinations, useful for assessment of scoliosis and for leg length, angulation, and deformity measurement and other diagnostic functions, require images that exceed the length of normal-sized radiographic films or other types of receiver media. In conventional practice, this extended- or long-length imaging (LLI) problem has been addressed using either of two basic approaches. The first approach uses an extra long, non-standard sized imaging detector. This approach is straightforward and feasible when using x-ray film as the imaging medium, but becomes costly and impractical when using various types of digital radiography media. With Computed Radiography (CR) media, in which a photostimulable phosphor storage sheet or plate is exposed and digitally scanned in separate operations, the dimensions of the storage medium can be constrained by the dimensions of the CR cassette that houses the medium. There may be some flexibility for extending the size of the CR medium, as taught, for example, in U.S. Pat. No. No. 5,130,541 entitled “METHOD OF AND APPARATUS FOR RECORDING AND READING RADIATION IMAGE” to Kawai that shows the use of an elongated CR plate for long-length imaging. However, this approach may prove impractical and the expense difficult to justify for most radiography installations.
For Digital Radiography (DR) detectors that directly transform received exposure energy to digital image data, the problem of extended-length imaging is much more complex and the fabrication and use of an oversized DR detector is seen as prohibitively costly and impractical. Instead, a second approach for extended-length imaging obtains portions of the full image on two or more standard-size detectors, adjusting the translational or angular position of the x-ray source between each image, then uses digital image processing to stitch the obtained sub-images together. This approach is taught, for example, in U.S. Pat. No. 5,111,045, entitled “APPARATUS FOR RECORDING AND READING RADIATION IMAGE INFORMATION” to Konno et al.; in U.S. Pat. No. 5,986,279, entitled “METHOD OF RECORDING AND READING A RADIATION IMAGE OF AN ELONGATE BODY” to Dewaele; and EPO 919856A1, entitled “METHOD AND ASSEMBLY FOR RECORDING A RADIATION IMAGE OF AN ELONGATE BODY” to Dewaele et al. A variation on this approach also sequentially re-positions a single DR detector along the anatomy to be imaged so that the same detector is used to obtain images at two or more positions.
Among the factors that make long-length imaging using a single DR detector more complex is the required image transfer and refresh timing of the DR detector hardware. Even with higher speed circuitry and advanced techniques for image storage and transfer, the time interval required between image captures is on the order of a few seconds. Inadvertent movement of the patient between images can present difficulties for reconstruction of the full length image from individual component images. The timing of DR exposure and detector and radiation source movement or adjustment between images provides significant complications for the designer of DR systems.
Due to the difficulty of this problem, solutions that have been proposed thus far generally require complex interaction and coordination between components that are shifted between positions for obtaining individual images. Translation of the imaging detector relative to the patient has been proposed using various techniques. For example, U.S. Pat. No. 4,613,983 entitled “METHOD FOR PROCESSING X-RAY IMAGES” to Yedid et al. and U.S. Pat. No. 5,123,056 entitled “WHOLE-LEG X-RAY IMAGE PROCESSING AND DISPLAY TECHNIQUES” to Wilson disclose X-ray systems for imaging a human subject lying on a table. Either the table or both the X-ray source and table are then moved to produce, in quick succession, a series of overlapping electronic images which are then combined into an elongated image for display or printing. Similarly, Warp et al. in U.S. Pat. No. 7,177,455 entitled “IMAGE PASTING SYSTEM USING A DIGITAL DETECTOR” teach shifting the position of a DR detector and adjusting the corresponding position of the x-ray source for obtaining individual images that can be stitched together using digital techniques.
As is noted in U.S. Pat. No. 6,944,265 entitled “IMAGE PASTING USING GEOMETRY MEASUREMENT AND A FLAT-PANEL DETECTOR” to Warp et al., a number of techniques have been developed for combining individual images in order to form a composite long-length image. Using various techniques, reference points using identifiable anatomy structures or other features common to two images can be used to properly align them. For most image-stitching routines, an overlap area, with anatomy common to both images is provided along the interface between two adjacent images.
Although techniques disclosed thus far may be workable for obtaining separate images of the patient that can then be stitched together, a number of practical problems remain. One problem of note relates to the amount of time that is required for DR detector response for providing image data following exposure. On-board processing by the DR detector, converting the stored energy for each pixel into equivalent digital data, can take a few seconds. A sizable amount of image data is generated for each image and must be transferred from the DR detector to an external host processor. Even with high-speed data links, it can take 10-15 seconds or longer to transfer the volume of data that is generated. Some improvement in transfer speeds can be anticipated; however, a measurable amount of time will still be required for image transfer and for re-positioning of the detector to the next imaging position. During the interval between images, the patient is likely to move, which complicates the processing task for stitching image data together.
Another problem relates to the relative complexity of conventional solutions for long-length imaging using digital radiography. Using a conventional DR system, for example, the task of moving the gantry-mounted detector and x-ray source to the appropriate positions can require precision re-positioning of a few hundred pounds of supporting hardware during the brief interval between individual images. Thus, in practice, it can be prohibitively difficult to implement some of the proposed long-length imaging solutions for existing DR equipment.
Therefore, it can be appreciated that there is a need for a long-length imaging solution that is streamlined in weight and mechanical complexity, relatively low cost, that reduces the time interval between images, and that reduces the complexity of combining image data at the interface between two different images.